In general, when cutting a metal or the like by using a laser beam, piercing is carried out at an initial cutting start point. The piercing is performed by irradiating a laser beam after a machining head is accurately placed at a piercing position.
FIG. 6 is a diagram illustrating the conventional piercing control mentioned above. In the figure, the horizontal axis indicates time t and the vertical axis indicates the speed V of movement of the machining head. After a previous cutting operation is completed, the machining head is accelerated from time t.sub.0 to time t.sub.10, then moved at a fixed speed from time t.sub.10 to time t.sub.20, and decelerated from time t.sub.20 to time t.sub.30, so as to be moved to the next cutting start point. Subsequently, positioning at the cutting start point is checked during a time period t.sub.30 -t.sub.40, and when the positioning completion is confirmed at time t.sub.40, piercing is carried out at that position. Simultaneously with completion of the piercing at time t.sub.50, the subsequent cutting operation is started. The interval t.sub.0 -t.sub.40 is a time period during which the machining head is moved to the next machining start point, the interval t.sub.40 -t.sub.50 is a time period for the piercing, and the cutting time period starts from t.sub.50.
Thus, the conventional piercing requires the time period t.sub.30 -t.sub.40 for confirmation of the positioning completion after deceleration according to motion control is ended.
Piercing is a machining operation executed at a start point for pre-machining within a portion that is irrelevant to the final shape of products, and accordingly, the piercing position need not be strictly set.
However, since the positioning for piercing is carried out with accuracy, as described above, the positioning requires the considerable time t.sub.30 -t.sub.40, which is not negligible in cases where shorter machining time is demanded.